Possible to limit filters ManyToMany/Foreign Key in Django admin for a model where the relationship is defined on the other model?

So the title is a bit obtuse, I know, but I couldn't think of a more succinct way to state it. Here's the issue:

I've created two proxy models for "user types", both inheriting from django.contrib.auth.User. Each has a custom manager limiting the queryset to items belonging to a particular Group. Specifically, there's a PressUser which is any user belonging to the "Press" group and StaffUser which is any user in any other group than "Press".

The issue is that when I add 'groups' to list_filters on my StaffUsers modeladmin, the resulting filter options are every group available, including "Press", and not just groups available to StaffUsers.

I've research a bit online and came up with a custom filterspec that should produce the behavior I want, but the problem is that the User model's 'groups' attribute is actually a related_name applied from the Group 开发者_如何学运维model. As a result, I can't attach my filterspec to 'groups' in my proxy model.

Is there any other way to apply the filterspec? Alternatively, is there a better approach to filtering the items returned by the default filterspec?

---

So, I was able to solve my own problem. For those that might run into a similar situation, here are the steps:

The approach I took is to modify the change_list.html template and manually filter out the items I didn't want to be included. There's quite a number of changes to make, though.

First, add a changelist_view method to your ModelAdmin:

# myproject/account/admin.py

class StaffUserAdmin(models.ModelAdmin):
    ...
    def changelist_view(self, request, extra_context=None):
        groups = Group.objects.exclude(name__in=['Press',]).values_list('name')
        extra_context = {
            'groups': [x[0] for x in groups],
        }
        return super(StaffUserAdmin, self).changelist_view(request,
            extra_context=extra_context)

Basically, all we're doing here is passing in the filtered list of Groups we want to use into the context for the template.

Second, create a change_list.html template for your app.

# myproject/templates/admin/auth/staffuser/change_list.html

{% extends "admin/change_list.html" %}

{% load admin_list %}
{% load i18n %}
{% load account_admin %}

{% block filters %}

    {% if cl.has_filters %}
    <div id="changelist-filter">
        <h2>{% trans 'Filter' %}</h2>
        {% for spec in cl.filter_specs %}
            {% ifequal spec.title 'group' %}
                {% admin_list_group_filter cl spec groups %}
            {% else %}
                {% admin_list_filter cl spec %}
            {% endifequal %}
        {% endfor %}
    </div>
    {% endif %}

{% endblock filters %}

This one deserves a little explanation. First, the template tag loads: admin_list is used for the default Django template tag responsible for rendering the filters, admin_list_filter, i18n is used for trans, and account_admin is for my custom template tag (discussed in a sec), admin_list_group_filter.

The variable spec.title holds the title of the field that's being filtered on. Since I'm trying to alter how the Groups filter is displayed, I'm checking if it equals 'groups'. If it does, then I use my custom template tag, otherwise, it falls back to the default Django template tag.

Third, we create the template tag. I basically just copied the default Django template tag and made the necessary modifications.

# myproject/account/templatetags/account_admin.py

from django.template import Library

register = Library()

def admin_list_group_filter(cl, spec, groups):
    return {'title': spec.title, 'choices' : list(spec.choices(cl)), 'groups': groups }
admin_list_group_filter = register.inclusion_tag('admin/auth/group_filter.html')(admin_list_group_filter)

The only things that I've changed here are adding a new argument to the method called 'groups' so I can pass in my filtered list of groups from before, as well as adding a new key to the dictionary to pass that list into the context for the template tag. I've also changed the template the tag uses to a new one that we're about to create now.

Fourth, create the template for the template tag.

# myproject/templates/admin/auth/group_filter.html

{% load i18n %}
<h3>{% blocktrans with title as filter_title %} By {{ filter_title }} {% endblocktrans %}</h3>
<ul>
{% for choice in choices %}
    {% if choice.display in groups %}
    <li{% if choice.selected %} class="selected"{% endif %}>
        <a href="{{ choice.query_string|iriencode }}">{{ choice.display }}</a></li>
    {% endif %}
{% endfor %}
</ul>

No big surprises here. All we're doing is putting all the pieces together. Each choice is a dictionary with all the values needed to construct the filter link. Specifically, choice.display holds the actual name of the instance that will be filtered by. Obviously enough, I've set up a check to see if this value is in my filtered list of groups I want to show, and only render the link if it is.

So, it's a bit involved but works remarkably well. Just like that, you have a list of filters that is exactly what you want instead of the default ones generated by Django.

---

I'm going to tell you off the bat that I've never done this before myself, so take it with a grain of salt.

What I'd suggest would be to override get_changelist on your ModelAdmin, to return a custom ChangeList class, which you can define somewhere in your admin module.

Your custom ChangeList class would simply override get_filters, so you can map your custom FilterSpec for the group field.

Another thing that might interest you are patches from the feature request ticket for specifying custom filter specs. The latest patch doesn't work for Django 1.3rc1 yet, although @bendavis78 recently posted that he's working on a new one, but depending on your version of Django it may apply cleanly.

It looks like it barely missed the cut to get included into the 1.3 milestone, so I figure it's going to make it into the trunk as soon as work beings on Django 1.4.